ssh: switch from parallel-ssh to ansible-pylibssh

Unfortunately, parallel-ssh has become a dead project incompatible
with python-3.12+. Some effort was created by its community to make
it compatible, unfortunately the only maintainer with write access
is unresponsive and there is not much hope for a new release.

Therefore we switch to ansible-pylibssh, which provides low level
libssh python bindings. There is significant performance impact
in artificial test case ("running 'exit 0' over and over again is twice
as slow) due to differences in poll implementation, however the impact
is neglitable in real world scenarios (~20 seconds delay on 350 test
cases). This small slowdown also provides a huge benefit in very small
CPU usage 0-1% where parallel-ssh keeps spinning on 10-11%.

pyproject.toml

@@ -35,7 +35,7 @@ files = ["requirements.txt"]
 source = "vcs"
 
 [[tool.mypy.overrides]]
-module = ["pssh.*", "pytest_output.*"]
+module = ["pylibsshext.*", "pytest_output.*"]
 ignore_missing_imports = true
 
 [tool.isort]